This type of device is employed notably in the field of generating high-order harmonics by laser-material interaction on a solid target, corresponding to the generation of an electromagnetic field of extremely short wavelength, of the order of a few tens of nanometers; these harmonics can be set in phase in order to generate pulses of attosecond length (in practice of the order of 10−17 or 10−16 second). Such radiation sources are desirable, for example, in the analysis of ultrafast phenomena on the subatomic scale.
There are currently harmonic sources obtained from the interaction of a femtosecond laser on a solid target, although these are produced with a low or very low repetition rate (<10 Hz). This is possible because the phenomenon of laser-material interaction generates a secondary beam which may typically be a harmonic beam, that is to say a light beam with a wavelength shorter than that of the primary source.
The problem encountered with this type of interaction of an ultra-intense laser on a solid target, when wishing to operate at a very high rate, is to be able to regenerate the interaction surface between each shot because each interaction leads to destruction of the interaction surface, and it is necessary for the light pulse of the primary source to interact with a fresh region on the target.
It is therefore necessary to provide means for displacing the target between each shot, so that the surface presented to the subsequent laser pulse is intact. Given that the focal point of the laser is fixed in space, one solution consists in using a disk-shaped target to which a rotational movement is imparted, so that the impacts of the laser on the target form a circle. Once the circle is completed, the target is translated parallel to the surface of the target then the rotational movement is restarted in order to obtain a circle concentric with the first, and so on. This method makes it possible to obtain a secondary source whose repetition rate is equal to that of the primary source.
Nevertheless, and this is inherent to the method employed, setting the target in movement creates instabilities in the emission of the secondary source, both in terms of the position of said secondary source (which also leads to an instability in the efficiency of the generation process) and in terms of the orientation of said source, while it is necessary to be able to provide a secondary source with high precision in terms of beam position and orientation.